The electronic control circuit is well suited for controlling a propulsion system of a lift truck or the electrical system of a log chipper and debarker.
In the lift truck, electric power is typically available to the electric drive motors and other components of the propulsion system as well as the lift mast when the key switch or other control switch is opened. It is desirable to positively disconnect the battery or power source from the vehicle systems when the key switch is opened to reduce the electrical hazard and to insure the vehicle systems do not unintentionally operate.
One solution to preventing the propulsion system from unintentionally operating is provided by U.S. Pat. No. 3,507,350 to Myron J. Boyajian dated Apr. 21, 1970. Boyajian uses a seat switch for a vehicle wherein the drive power to the traction means is interrupted upon the operator leaving his operating station and wherein the control prevents unintentional movement of the vehicle upon the return of the operator to his operating station. The seat switch, however, does not interrupt the power flow at the power supply.
In the log chipper and debarker, logs often become lodged and the log chipper cannot operate. When this happens, it is desirable to positively interrupt the flow of power to the log chipper so that the log can be safely removed.
The lift truck and log chipper sometimes have a main circuit breaker which trips and interrupts the current flow only when current of a preselected magnitude flows through the circuit breaker. The circuit breaker positively interrupts the current flow when an overload condition exists, but does not do so when the vehicle or log chipper is merely stopped or when a non-operating condition exists. It is therefore desirable to trip the circuit breaker whenever any one of a plurality of non-operating conditions exists.